1. Field of the Invention
The present invention relates to a surface lighting device, and more particularly to a surface lighting device using light emitting diodes as light source.
2. Description of the Related Art
Light emitting diodes (LEDs) have many advantages, such as high luminance brightness, low power consumption, good compatibility with integrated circuit, long-term reliability and environment friendliness compared with other conventional lighting devices. Thus, LEDs have been widely used as backlight source for liquid crystal display (LCD), light source for vehicle lamps and luminance devices, as described in an article titled “Unique White LED Packaging Systems” cited in a publication of 2003 IEEE Electronic Components and Technology Conference written by Atsushi Okuno.
In related art, LED surface lighting device is divided into edge type and direct type according to LED positions. In the direct type LED surface lighting device, LEDs are arranged at a bottom of a light guiding plate for supplying light rays. However, a size of the LED surface lighting device currently becomes larger and larger, and correspondingly it is required to increase size of the light guiding plate and number of the LEDs used in the light source device. Accordingly, cost of the direct type LED surface lighting device increases.
Referring to FIG. 9, an edge type LED light source module 420 comprises a light guiding plate 422 and two LEDs 424 arranged at lateral sides 4220 of the light guiding plate 422. Light rays emitted from the LEDs 424 enter into the light guiding plate 422 from the lateral sides 4220, and then emit out of a light emitting surface 4222 adjacent to the lateral sides 4220.
Referring to FIG. 10, a surface lighting device 400 having a large size is formed by assembling a plurality of the LED light source modules 420 side-by-side. Light rays from the LEDs 424 at the lateral sides 4220 of a single LED light source module 420 can only emit towards the opposite lateral sides 4220 and out of the light emitting surface 4222 of the single LED light source module 420. The light rays cannot arrive at a seam area 430 between two adjacent LED light source modules 420. Thus, a dark area is formed above the seam area 430 so that illumination uniformity of the surface lighting device 400 cannot be satisfactorily obtained.
Accordingly, what is needed is a LED surface lighting device having a satisfactory illumination uniformity.